Impact of HF coupler on HF mesh networking

High frequency (HF) operations require large antennas. For example, at three megahertz, a system would require a minimum thirty-foot antenna. A typical broadband antenna for large fixed-site stations may by 110 ft (34 m) and constrain impedance mismatch loss to 2:1 (the impedance mismatch loss across the HF frequency band, two to thirty MHz, is less than 0.5 dB even with no antenna coupler). The spectrum sensor/HF Receiver connected to such a broadband antenna only suffers a 0.5 dB penalty.

Such antennas are too large for mobile platforms. Mobile platforms utilize electrically short antennas with high variable impedance across the HF band. In order to efficiently couple the transmitted power from the power amplifier to the antenna, an impedance matching device known as an HF coupler is used. The HF coupler limits impedance mismatch loss to less than 0.17 dB, but the HF coupler narrows the operating frequency range; the tuning bandwidth is frequency dependent; and the HF coupler is only 70% efficient (i.e., it burns 30% of the power exchanged internal to the coupler in the form of heat).

To implement an ad-hoc HF mesh network, each HF node must have a spectral sensor. The spectrum sensor must be able to access the entire HF spectrum to detect all propagating frequencies from all participants in the network, but the HF coupler limits the spectral view of the sensor. In an HF mesh network with mobile nodes using an HF coupler, the coupler bandwidth is around 3 kHz at 2 MHz and bandwidths of 48 KHz can only be supported for frequencies above 11 MHz. The maximum coupler bandwidth supportable at 30 MHz is less than 100 KHz. Certain network requirements can only be satisfied via a hub and spoke network with fixed site nodes being the central hubs with spectral sensors. The HF coupler at all disadvantaged nodes limits the view of the spectral sensor to the coupler bandwidth at the tuned frequency. In contested theaters, such architecture is unsupportable.

It would be advantageous to have a system and method to enable HF mesh networks with mobile platforms and broad frequency capability without fixed stations.

In one aspect, embodiments of the inventive concepts disclosed herein are directed to an HF mesh network connectivity algorithm that incorporates the impact of coupler efficiency in the transmit direction and impact of impedance mismatch on the receive direction. Nodes in the HF mesh network include an HF coupler; the HF coupler switches between an impedance matching path and a bypass path. The impedance matching path may be used to transmit while the bypass path is used to receive over a wider spectrum then is enabled with impedance matching.

Configuration files include antenna configuration and the coupler configuration files. A routing table may be configured to consider only bi-directional links for connectivity or use composite link margin to route using unidirectional paths if end-to-end connectivity can be found. The transmit and receive paths can be different and may use different frequencies.

In a further aspect, the impedance matching path may be utilized for certain narrow bandwidth receive operations.

In a further aspect, the bypass path enables a spectral sensor to see all propagating frequencies.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and should not restrict the scope of the claims. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the inventive concepts disclosed herein and together with the general description, serve to explain the principles.

Before explaining various embodiments of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. In the following detailed description of embodiments of the instant inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art having the benefit of the instant disclosure that the inventive concepts disclosed herein may be practiced without these specific details. In other instances, well-known features may not be described in detail to avoid unnecessarily complicating the instant disclosure. The inventive concepts disclosed herein are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

As used herein a letter following a reference numeral is intended to reference an embodiment of a feature or element that may be similar, but not necessarily identical, to a previously described element or feature bearing the same reference numeral (e.g.,,,). Such shorthand notations are used for purposes of convenience only, and should not be construed to limit the inventive concepts disclosed herein in any way unless expressly stated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of “a” or “an” are employed to describe elements and components of embodiments of the instant inventive concepts. This is done merely for convenience and to give a general sense of the inventive concepts, and “a” and “an” are intended to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Also, while various components may be depicted as being connected directly, direct connection is not a requirement. Components may be in data communication with intervening components that are not illustrated or described.

Finally, as used herein any reference to “one embodiment,” or “some embodiments” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the inventive concepts disclosed herein. The appearances of the phrase “in at least one embodiment” in the specification does not necessarily refer to the same embodiment. Embodiments of the inventive concepts disclosed may include one or more of the features expressly described or inherently present herein, or any combination or sub-combination of two or more such features.

Broadly, embodiments of the inventive concepts disclosed herein are directed an HF mesh network connectivity algorithm that incorporates the impact of coupler efficiency in the transmit direction and impact of impedance mismatch on the receive direction. Nodes in the HF mesh network include an HF coupler; the HF coupler switches between an impedance matching path and a bypass path. The impedance matching path may be used to transmit while the bypass path is used to receive over a wider spectrum then is enabled with impedance matching. The impedance matching path may be utilized for certain narrow bandwidth receive operations. The bypass path enables a spectral sensor to see all propagating frequencies.

Many platforms have only a single electrically short HF antenna. It is practically difficult for these platforms to receive HF communications while transmitting without additional equipment to support simultaneous operations. Fixed site nodes use split-site architecture where the transmitter and receiver are separated by tens of miles to prevent the transmitter from blinding the receiver so that full duplex communication is possible. Because of power limitations, the HF coupler cannot be bypassed during transmission.

Referring to, block diagrams of a mesh network,according to an exemplary embodiment are shown. Where an HF coupler with an impedance matching element is used (as illustrated in), nodes,,,,,may have sufficient bandwidth/signal strength for bidirectional communication. However, with impedance mismatch loss (as illustrated in), some excluded nodesmay be effectively removed from the mesh network,, as even though certain nodes,can receive transmissions from the excluded node, there are no nodes,,,,that send transmissions to the excluded node. Furthermore, isolated nodescannot directly communicate with certain neighboring nodes,, but can communicate with them using multi-hop relaying.

Every node,,,,,may be associated with one or more antenna configuration files. A node,,,,,can be associated with multiple antenna configuration files because some platforms may have multiple HF antennas and the appropriate antenna configuration file may be selected for a given mission. In at least one embodiment, an antenna configuration may be defined by the frequency, gain, and mismatch loss in dB. Antenna gain values may be averaged values that may have +/−5 dB variation due to angular variation in the antenna pattern. Antenna gain varies depending on the direction of the destination node, launch angle, frequency, etc. In at least one embodiment, antenna gain configuration may be dependent on azimuth or elevation angles and frequency. A gain table may have multiple frequency and angle pairs to obtain a better antenna gain. Because communication often relies on different elevation angles between nodes, it may be impossible to find a single frequency where all nodes will be able to communicate. It is desirable for nodes to be able to hear on all frequencies.

Referring to, a block diagram of an HF couplersuitable for implementing exemplary embodiments is shown. The HF couplerdefines a transmit path with a high-performance exciter according to transmit specifications of legacy 3 kHz radios, and also includes a 48 KHz wideband transmit path. The HF coupleralso defines a receive path that may accept impedance matched coupler input from an impedance matching elementor direct input from an antenna.

Where a wideband receiver receives an impedance matched input, the wideband receiver can only see the coupler bandwidth. If the impedance matching elementis bypassed, then the wideband receiver can see the entire frequency range (e.g., 2 MHz to 30 MHz). The impedance matching elementmay be bypassed via a switchthat may generally function as a transmit/receive switch, but that in certain situations it may be advantageous not to bypass the impedance matching elementin a receive mode.

Propagation tools may ignore the impact of the HF couplerduring transmission. Mismatch loss is on the order of 0.2 dB. Furthermore, HF couplers have efficiencies that range between 70% and 90% depending on frequency and power handling capacity. In contested environments, a potential 20+% power loss has to be accounted for during transmission, to ensure that jamming threats can be overcome.

It may also be advantageous to consider impedance mismatch loss during receive. Such impedance mismatch loss becomes important in both contested and uncontested environments. Frequency dependent mismatch loss variations can be very large and cannot be ignored when the HF coupleris bypassed during receive. Such loss is an unavoidable result of allowing a spectral sensorto see outside the HF coupler bandwidth. Impedance mismatch losses can alter the frequencies that propagate between nodes and also introduce unidirectional connectivity.

HF coupler efficiency is dependent on the frequency of operation and power handling capacity of the HF coupler. Frequency dependent HF coupler efficiency may enable a more accurate determination of the power transferred from a power amplifier to the antennaduring transmit as compared to a average 70% value used in simulations. Antenna configuration parameters determine whether an average coupler efficiency or frequency dependent coupler efficiency is used.

Referring to, a block diagram of an HF software defined radiosuitable for implementing exemplary embodiments is shown. The HF software defined radiodefines a transmit path including a high-performance exciteraccording to transmit specifications of legacy 3-kHz radios, and also includes a 48-kHz wideband transmit path. The HF software defined radioalso defines a receive path (the paths accessible via a switch) that may accept impedance matched coupler input or the direct antenna input.

In at least one embodiment, the receive path may include a receiverconfigured for a relatively narrow bandwidth (e.g., 3 kHz to 48 KHz) to receive signals when an HF coupler is used in the receive path, and a receiverconfigured for a relatively wide bandwidth (e.g., 2 MHz to 30 MHz) to receive signals when the HF coupler is bypassed. In at least one embodiment, the wide bandwidth receivermay be in data communication with an external spectrum sensor.

Ad-hoc mesh network waveforms may be capable of interfacing with spectrum sensors, either integrated into the HF software defined radioor external. The waveform supports both active node discovery using channel sounding and/or passive node discovery using the spectrum sensorin conjunction with integrated Voice of America Coverage Analysis Program (VOACAP). Route management functionality may consider the impact of HF coupler efficiency during transmission and also accounts for antenna gain in the direction of the HF receiver nodes.

Referring to, a block diagram of an HF software defined radiosuitable for implementing exemplary embodiments is shown. The HF software defined radiodefines an impedance match path including a switchconnected to a high-performance exciterto transmit and a relatively narrow bandwidth receiver. The impedance match path is connected to an impedance matching element of an HF coupler. Furthermore, the HF software defined radiodefines an impedance bypass path including a relatively wide bandwidth receiver. In at least one embodiment, the wide bandwidth receivermay be in data communication with an external; spectrum sensor. Such embodiment enables simultaneous reception of an impedance matched and bypassed path so that the HF receiverperformance of 3 kHz and 48 KHz paths are not compromised.

Referring to, a flowchart of a method for producing a routing table, and routing tables, according to exemplary embodiments are shown. Nodes in an HF mesh network determine ad-hoc mesh connectivity between all transmit/receive pairs, including HF coupler efficiency and the antenna mismatch losses due to bypassing the HF coupler during receive. Each node iteratively selectstransmit/receive pairs from a database of nodes in the HF mesh network, and iteratively selectsa frequency from frequency table. The node computeseffective radiated power (EIRP) for the transmit/receive pair and frequency, including coupler efficiency and antenna gain, and computesa 90% reliability path loss between the transmitter and receiver using an HF propagation tool such as VOACAP. Based on the EIRP and reliability path loss, the node computesa received signal strength and computesa corresponding receive sensitivity. If the node determinesif the receive signal strength is greater than the receive sensitivity, the transmit/receive pair and frequency are stored in a routing table as a potential frequency; in at least one embodiment, an associated link margin may be recorded if available. The process is repeated as long as the node determinesthere are more potential frequencies, or determinesthere are more transmit/receive pairs.

In at least one embodiment, the method produces a routing table (as in) having entries corresponding to a combination of frequency and link margin available for every transmit/receive pair. Such entries correspond to directly connected (“one-hop”) nodes. It may be appreciated that entries are directional in nature.

Each node may then determine indirect routes to all nodes that can be reached (as in). Entries may include intervening nodes. For example, a first entrymay include direct links from a first node to a second nodes and indirect links including intervening nodes; while a second entrymay include only indirect links from the second node to the first node.

The routing table may be created via predictive VOACAP connectivity, ad-hoc mesh connectivity determining techniques, ALE probes, or the like. If ad-hoc mesh connectivity techniques are used, then only direct connectivity for a node can be determined. In at least one embodiment, nodes may periodically exchange local routing tables to ensure that all nodes in the network can determine the connectivity to every other node in the network. Nodes may establish entries for indirect connection by combining local routing tables.

Unlike traditional routing tables, where connectivity between nodes implies bi-directional connectivity, in an HF mesh network the connectivity can be unidirectional due to antenna impedance mismatch which can be different in the receive direction as it is dependent on the antenna used on the platform. Entries in the routing table are therefore direction dependent.

In at least one embodiment, each routing table entry with more than one path may be ordered based on link margin for every transmit/receive pair. Where indirect paths exist, the node may determine composite end-to-end link margin.

Referring to, flowcharts of methods according to an exemplary embodiment are shown. During a routing table discovery/production process (as set forth in), nodes in an HF mesh network may computeEIRP for each transmit/receive pair and frequency. To computeEIRP, including HF coupler efficiency and mismatch loss due to bypass, the node may extracttransmit power, HF coupler efficiency, and transmit antenna gain. Effective transmit power is computedas the product of transmit power and HF coupler efficiency. Then effective transmit beam power is computed, for example as the weighted log of the effective transmit power (e.g., 10*log effective transmit power*1000). The EIRP, including HF coupler efficiency, can then be computedas the sum of the effective transmit beam power and transmit antenna gain.

In at least one embodiment, nodes in an HF mesh network may computea 90% reliability path loss between the transmitter and receiver using an HF propagation tool. To computereliability path loss, the node may extracttransmitter and receiver longitude and latitude, frequency, and time. Reliability is defined(e.g., 90%), and a distance loss profile is appliedfor a given propagation tool such as VOACAP. The path loss may then be extracted.

In at least one embodiment, nodes in an HF mesh network may computea received signal strength. The node extractsEIRP, path loss, path loss margin, frequency, receiver antenna gain, and receiver mismatch loss. Received signal strength is then determine as EIRP minus path loss and path loss margin, plus receiver antenna gain minus receiver mismatch loss.

Embodiments of the present disclosure are useful during solar flares including bursts of X-ray and ultra violet radiation. Such emissions ionize the ionosphere which affects HF propagation in the range of few dB to total blackout on one or more frequencies in the frequency table. The impact is regional, variable in intensity based on location, and frequency dependent; lower frequencies are affected more than higher frequencies. Solar flare updates may be received via an internet connection or via other HF nodes in the network.

Active route management techniques like ALE or waveform-initiated channel sounding may automatically incorporate the impact of solar flares as frequencies that are excessively penalized will not propagate hence are not used. If passive VOACAP predictions are used to determine connectivity between HF nodes, then frequency dependent loss due to solar flares should be accounted for. If an HF node is configured to receive solar flare notification, then the link budget may consider the frequency dependent solar flare loss. If a node is configured to account for solar flare impact, computingreceived signal strength includes the frequency dependent loss in the link budget.

In at least one embodiment, nodes in an HF mesh network may computereceive sensitivity. The node extractsfrequency, bandwidth, and signal-to-noise ratio. If the node determinesthat the frequency is less than or equal to some threshold (e.g., 10 MHz), receiver noise is setto some environmental noise based on the frequency; if the node determinesthat the frequency is greater than the threshold, receiver noise is setto some noise value. The node then calculatesreceive sensitivity based on the sum of a predetermine threshold, a weighted log of bandwidth, the receiver noise, the signal-to-noise ratio, and some margin.

Embodiments of the present disclosure are useful during solar flares including bursts of X-ray and ultra violet radiation. Such emissions ionize the ionosphere which affects HF propagation in the range of few dB to total blackout on one or more frequencies in the frequency table. The impact is regional, variable in intensity based on location, and frequency dependent; lower frequencies are affected more than higher frequencies. Solar flare updates may be received via an internet connection or via other HF nodes in the network.

Active route management techniques like ALE or waveform-initiated channel sounding may automatically incorporate the impact of solar flares as frequencies that are excessively penalized will not propagate hence are not used. If passive VOACAP predictions are used to determine connectivity between HF nodes, then frequency dependent loss due to solar flares should be accounted for. If an HF node is configured to receive solar flare notification, then the link budget may consider the frequency dependent solar flare loss. If a node is configured to account for solar flare impact, computing received signal strength includes the frequency dependent loss in the link budget.

Embodiments of the present disclosure enable ad-hoc HF mesh network connectivity by allowing the spectral sensor/HF Receiver to see the entire HF spectrum (2.0 MHz-30.0 MHz). Ad-hoc HF mesh network connectivity forces all HF nodes on constrained platforms to bypass the HF coupler during receive. Bypassing the coupler mates the frequency dependent variable impedance antenna to a 50 Ohm receiver. Embodiments incorporate HF coupler efficiency, impedance mismatch loss, and direction dependent antenna gain when determining transmit power actually going out.

It is believed that the inventive concepts disclosed herein and many of their attendant advantages will be understood by the foregoing description of embodiments of the inventive concepts, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components thereof without departing from the broad scope of the inventive concepts disclosed herein or without sacrificing all of their material advantages; and individual features from various embodiments may be combined to arrive at other embodiments. The forms herein before described being merely explanatory embodiments thereof, it is the intention of the following claims to encompass and include such changes. Furthermore, any of the features disclosed in relation to any of the individual embodiments may be incorporated into any other embodiment.